1. Field of the Invention
The present invention relates to motor control systems and methods and, more particularly, to motor control systems and methods for generating a motion profile of a motor.
2. Description of Related Art
Motor control is a requirement for most industrial motorized systems, such as robotic systems or semiconductor manufacturing systems. For most motor control systems it is important to correctly generate the profile of a motor. The profile of a motor refers to the time dependent relationships of the rotational velocity and rotational angle of the motor.
FIG. 1 is a block diagram of a conventional motor control circuit. As shown in FIG. 1, the conventional motor controlling circuit includes a motor 11, a profile generator 12, a subtractor 13, a feed-back controller 14, an adder 15, and a feed-forward controller 16. Profile generator 12 receives positional data from motor 11 and outputs acceleration data (a), velocity data (v), and displacement data (s) of motor 11. Subtractor 13 subtracts the positional data of motor 11 from the displacement data (s) output by profile generator 12. Feed back controller 14 receives the output of subtractor 13 and generates a feed back control signal. Feed forward controller 16 receives the acceleration data (a) and the velocity data (v) output by profile generator 12 and generates a feed forward control signal. Adder 15 adds the positional data of motor 11, the feed back and feed forward control signals, and outputs a control signal to motor 11.
In the above-described motor control circuit, motor 11 has a constant rate of acceleration or deceleration and operates at constant rates of speed. Profile generator 12 determines the acceleration, deceleration and velocity of motor 11 based on profile data for the acceleration data (a), velocity data (v) and displacement data (s).
Conventional profile generating methods for use in profile generator 12 can be divided into two general types. First, a software-based method may be used to determine the velocity profile using a polynomial profile generating function that models velocity with respect to time. The profile generating function is stored in a memory and can be used to determine a velocity data at a given point in time. Preferably, the polynomial function has a high order so that the velocity profile can be accurately modeled. However, the calculation time increases almost exponentially with the order of the polynomial. Thus, this method is time intensive making it impractical for many industrial applications.
The second profile generating method is a hardware-based method that generates the velocity profile through a digital circuit. Examples of this type of method are disclosed in U.S. Pat. No. 4,554,497, entitled Acceleration/Deceleration Circuit, and U.S. Pat. No. 4,554,758, entitled Method and Apparatus for Controlling the Acceleration and Deceleration of a Movable Element Without Abrupt Changes in Motion. Under the hardware-based method, however, the velocity profile is fixed by the hardware. Another drawback is that it is difficult to make the profile for an acceleration interval different from that for a deceleration interval.